This invention relates generally to manufacture of electronic components, and more specifically to manufacturing of magnetic components such as inductors.
A variety of magnetic components, including but not limited to inductors and transformers, include at least one winding disposed about a magnetic core. In some components, a core assembly is fabricated from ferrite cores that are gapped and bonded together. In use, the gap between the cores is required to store energy in the core, and the gap affects magnetic characteristics, including but not limited to open circuit inductance and DC bias characteristics. Especially in miniature components, production of a uniform gap between the cores is important to the consistent manufacture of reliable, high quality magnetic components.
In some instances, epoxies have been used to bond the ferrite cores used to produce the bonded core assembly for magnetic components. In an effort to consistently gap the cores, non-magnetic beads, typically glass spheres, are sometimes mixed with adhesive insulator materials and dispensed between the cores to form the gap. When heat cured, the epoxy bonds the cores and the beads space the cores apart to form the gap. The bond, however, is primarily dependant upon the viscosity of the epoxy and the epoxy to beads ratio of the adhesive mix dispensed between the cores. It has been noted that in some applications the bonded cores are insufficiently bonded for their intended use, and controlling the epoxy to glass spheres ratio in the adhesive mix has proven very difficult.
In another type of magnetic component, a non-magnetic spacer material is placed between two magnetic core halves, and the core halves are then fastened together to hold the spacer material in place. The spacer material is frequently made of a paper or mylar insulator material. Typically, the core halves and spacer are secured to one another with tape wrapped around the outside of the core halves, with an adhesive to secure the core halves together, or with a clamp to secure the core halves and keep the gap located between the core halves. Multiple (more than two) pieces of spacer material are rarely used, since the problem of securing the structure together becomes very complicated, difficult and costly.
Still another type of magnetic component includes a gap ground into one section of a core half, and remaining sections of the core half are fastened to another core half with any of the foregoing techniques.
Yet another method of creating a gap in core structures begins with a single piece core, and a slice of material is cut from the core (typically a toroid shaped core). The gap is frequently filled with an adhesive or epoxy to restore the strength and shape of the core.
Recently, composite magnetic ceramic toroids have been developed that include layered magnetic constructions separated by a nonmagnetic layer to form a gap. See, for example, U.S. Pat. No. 6,162,311. Bonding material (e.g., adhesives) and external gapping material (e.g. spacers) for magnetic core structures may therefore be eliminated.
In any of the foregoing devices, a conductor is typically placed through the core to couple energy into the core in the form of magnetic flux, and magnetic flux lines cross through and around the gap to complete a magnetic path in the core. If the conductor intersects the flux lines, a circulating current is induced in the conductor. Resistance of the conductor creates heat as the current circulates, which reduces the efficiency of the magnetic component. Moving the conductor farther away from the magnetic flux lines can reduce the amount of energy that is coupled to the conductor and hence increase the efficiency of the component, but this typically entails increasing the size of the component, which is undesirable from a manufacturing perspective.
Also, known magnetic components are typically assembled on a single core structure. When multiple inductors are employed, for example, the cores must be physically separated to prevent interference with one another in operation. Separation of the components occupies valuable space on a printed circuit board.
It is therefore desirable to provide a magnetic component of increased efficiency and improved manufacturability for circuit board applications without increasing the size of the components and occupying an undue amount of space on a printed circuit board.